1. Field of the Invention
The present invention relates to an optical cell. More particularly, the invention provides a flow-through optical cell in which changes in the dimension of component materials induced by changes in temperature are non-actively compensated to ensure that a sample gap of the sample space remains nearly constant, permitting reproducible spectroscopy despite variations in temperature.
2. Description of the Related Art
Prior optical cells do not mitigate effects of linear expansion of their components, such as U.K. Published Patent Application Number 2,071,355. Some prior optical cells have other problems, such as U.S. Pat. No. 6,490,034 to Woias and Hillerich, in which the optical path length within the cell is not adjustable.
Prior optical cells also do not permit ready sample placement and change of fluids in the sample space. See “Quantitative Measurement of the IR Spectra of Water Solutions” by N. N. Kal'nin and S. Yu Ven'yaminov, Zhurnal Prikladnoi Spektroskopii, 49(4) (1988) pp. 592-597. Only one sample gap distance can be achieved with a given base; a separate base must be machined for each sample gap to be investigated. Because there are no inlets in the cover or in the well, once a sample is contained in the sample space, bath fluid or a fluid sample in the sample space cannot be exchanged with another bath fluid or fluid sample without separating the cover and the base, introducing reproducibility. See also U.K. Published Patent Application Number 2,261,285, which uses solid samples sealed in a silicon-based sample space.
Light spectra of certain samples can be obtained with the attenuated total reflection technique (ATR). The ATR technique has several drawbacks. For example, only samples that can be brought into close contact with the optical element can be investigated; among solid samples, only samples that can be polished very flat can be studied. Investigation of solid samples with an irregular surface with ATR can be difficult or impossible.